Whether it is through ignorance or by reason of amnesia many Roman Catholics labor under the illusion - fostered by their hierarchy - that their church has always believed and acted in the past the way the benign way that it may act now, when in fact that same Catholic Church has believed the very opposite of what it does now and acted accordingly.
Here is the perfect illustration of that truth :

the History of the Roman Catholic Church's
official views on Human Slavery:

Who can deny the influence of the epistles of St. Paul on the church?

{ Titus 2:9-10 : } "Tell slaves to be submissive to their masters and to give satisfaction in every respect; they are not to talk back, not to pilfer, but to show complete and perfect fidelity, so that in everything they may be an ornament to the doctrine of God our Savior."

{ Ephesians 6: 5-8 : } "Slaves, obey your earthly masters with fear and trembling, in singleness of heart, as you obey Christ; not only while being watched, and in order to please them, but as slaves of Christ, doing the will of God from the heart. Render service with enthusiasm, as to the Lord and not to men and women, knowing that whatever good we do, we will receive the same again from the Lord, whether we are slaves or free."

{ 1 Cor. 7: 21–24 : } "Were you a slave when called? Do not be concerned about it. Even if you can gain your freedom, make use of your present condition now more than ever. For whoever was called in the Lord as a slave is a freed person belonging to the Lord, just as whoever was free when called is a slave of Christ. You were bought with a price; do not become slaves of human masters. In whatever condition you were called, brothers and sisters, there remain with God."

{ 1 Tim. 6:1-5 : } "Let all who are under the yoke of slavery regard their masters as worthy of all honor, so that the name of God and the teaching may not be blasphemed. Those who have believing masters must not be disrespectful to them on the ground that they are members of the church; rather they must serve them all the more, since those who benefit by their service are believers and beloved. Teach and urge these duties.Whoever teaches otherwise and does not agree with the sound words of our Lord Jesus Christ and the teaching that is in accordance with godliness, is conceited, understanding nothing, and has a morbid craving for controversy and for disputes about words. From these come envy, dissension, slander, base suspicions, and wrangling among those who are depraved in mind and bereft of the truth."

And now for Roman Catholic "TRADITION",
the teaching transmitted through the generations :
( supposedly from Jesus Christ )

362 AD

The local Council at Gangra in Asia Minor
excommunicates anyone encouraging a slave to despise his master or withdraw
from his service. (Became part of Church Law from the 13th
to 20th centuries).

354-430 AD

St. Augustine teaches that the institution of
slavery derives from God and is beneficial to slaves and masters. (Quoted by
many later Popes as proof of "Tradition".

650 AD

Pope Martin I condemns people who teach slaves
about freedom or who encourage them to escape.

1089 AD

The Synod of Melfi under Pope Urban II imposed
slavery on the wives of priests. (Became part of Church Law from the
13th century).

1179 AD

The Third Lateran Council imposed slavery on those
helping the Saracens.

1226 AD

The legitimacy of slavery is incorporated in the
Corpus Iuris Canonici, promulgated by Pope Gregory IX which remained
official law of the Church until 1913. Canon lawyers worked out four "just
titles" for holding slaves: slaves captured in war, persons condemned to slavery
for a crime; persons selling themselves into slavery, including a father
selling his child; children of a mother who is a slave.

1224-1274 AD

St.Thomas Aquinas defends slavery as instituted by
God in punishment for sin, and justified as being part of the right of
nations and natural law. Children of a slave mother are rightly slaves
even though they have not committed personal sin! (Quoted by many later
Popes).

1435 AD

Pope Eugenius IV condemns the indiscriminate
enslavement of natives in the Canary Islands, but does not condemn slavery as
such.

1450's AD

Pope Nicholas V issued the papal bull Dum Diversas on 18 June, 1452. It authorised (King) Alfonso V of Portugal to reduce any "Saracens (Muslims) and pagans and any other unbelievers to perpetual slavery.
The same pope wrote the bull Romanus Pontifex on January 5, 1455 to the same Alfonso. As a follow-up to the Dum diversas, it extended to the Catholic nations of Europe dominion over discovered lands during the Age of Discovery. Along with sanctifying the seizure of non-Christian lands, it encouraged the enslavement of native, non-Christian peoples in Africa and the New World.
"We weighing all and singular the premises with due meditation, and noting that since we had formerly by other letters of ours granted among other things free and ample faculty to the aforesaid King Alfonso – to invade, search out, capture, vanquish, and subdue all Saracens and pagans whatsoever, and other enemies of Christ wheresoever placed, and the kingdoms, dukedoms, principalities, dominions, possessions, and all movable and immovable goods whatsoever held and possessed by them and to reduce their persons to perpetual slavery, and to apply and appropriate to himself and his successors the kingdoms, dukedoms, counties, principalities, dominions, possessions, and goods, and to convert them to his and their use and profit – by having secured the said faculty, the said King Alfonso, or, by his authority, the aforesaid infante, justly and lawfully has acquired and possessed, and doth possess, these islands, lands, harbors, and seas, and they do of right belong and pertain to the said King Alfonso and his successors".

1493 AD

Pope Alexander VI authorises the King of Spain to
enslave non-Christians of the Americas who are at war with Christian
powers.

1537 AD

Pope Paul III condemns the indiscriminate
enslavement of Indians in South America.

1548 AD

The same Pope Paul III confirms the right of clergy
and laity to own slaves.

1639 AD

Pope Urban VIII denounces the indiscriminate
enslavement of Indians in South America, without denying the four just
titles for owning slaves.

1741 AD

Pope Benedict XIV condemns the indiscriminate
enslavement of natives in Brazil, but does not denounce slavery as such, nor
the importation of slaves from Africa. AD

1807

(Protestant) Britain became the first major power to permanently abolish the slave trade.
[ http://en.wikipedia.org/wiki/Haitian_Revolution#
Situation_in_1789 ] .

Following its Civil War, the United States of America enacted the 13th amendment to its Constitution banning slavery forevermore in this country.

That same year, the highest authority in the Catholic Church, short of the Pope, i.e. the "Holy Office" (of the Inquisition), which rules on matters of orthodox faith and teaching, declared published the following official statement, signed by then Pope,
Pius IX :
: "Slavery itself, considered as such in its essential
nature, is not at all contrary to the natural and divine law, and there can be
several just titles of slavery, and these are referred to by approved
theologians and commentators of the sacred canons It is not contrary to
the natural and divine law for a slave to be sold, bought, exchanged or
given". [Instruction 20, June 1866 ]

The turnaround

1888 AD

Pope Leo XIII condemns slavery in more general
terms, and supports the anti-slavery movement.

1918 AD

The new Code of Canon Law promulgated by Pope
azaa Benedictus XV condemns selling any person as a slave. (There is no
condemnation of owning slaves, however, and that was viewed as an entirely distinct issue at the time!).

1965 AD

The Second Vatican Council defends basic
human rights and denounces all violations of human integrity, including slavery
(Gaudium et Spes, no 27,29,67).